Neural stimulation system to prevent simultaneous energy discharges

ABSTRACT

Various aspects of the present subject matter relate to a system. Various embodiments of the system comprise at least one port to connect to at least one lead with at least one electrode, at least one stimulator circuit and at least one controller. The at least one stimulator circuit is connected to the at least one port and is adapted to deliver neural stimulation to a neural stimulation target using the at least one electrode. The at least one controller is adapted to determine when another energy discharge other than the neural stimulation to the neural stimulation target is occurring and to prevent delivery of the neural stimulation simultaneously with the other energy discharge. Other aspects and embodiments are provided herein.

CLAIM OF PRIORITY

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. patent application Ser. No. 11/110,542, nowissued as U.S. Pat. No. 7,881,782, filed on Apr. 20, 2005, which ishereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

This application relates generally to medical devices and, moreparticularly, to neural stimulation systems, devices and methods.

BACKGROUND

Direct electrical stimulation of parasympathetic nerves can activate thebaroreflex, inducing a reduction of sympathetic nerve activity andreducing blood pressure by decreasing vascular resistance. Sympatheticinhibition and parasympathetic activation have been associated withreduced arrhythmia vulnerability following a myocardial infarction,presumably by increasing collateral perfusion of the acutely ischemicmyocardium and decreasing myocardial damage. Modulation of thesympathetic and parasympathetic nervous system with neural stimulationhas been shown to have positive clinical benefits, such as protectingthe myocardium from further remodeling and predisposition to fatalarrhythmias following a myocardial infarction.

Different types of therapies can be delivered to treat a condition or totreat different conditions. For example, some neural stimulationtherapies involve stimulating two or more neural stimulation targets.Additionally, it possible to deliver both neural stimulation (NS)therapy and cardiac rhythm management (CRM) therapy for some conditions.Some CRM therapies involve stimulating two or more cardiac sites. Sometherapies apply pulses to measure an impedance across tissue, and usethe impedance measurement to provide a sensed feedback to control thetherapies. Thus, therapies can use multiple electrodes to apply currentthrough tissue for the neural stimulation and CRM therapies, and forimpedance measurements.

SUMMARY

The present subject matter addresses undesirable interactions that mightoccur when neural stimulation and another energy discharge occursimultaneously. The neural stimulation has an intended current paththrough tissue, and the other energy discharge has an intended currentpath through tissue. However, unintended current paths can occur betweenelectrodes when the neural stimulation and the other energy dischargeoccur simultaneously. The other energy discharge can be for therapy ordiagnostic purposes. Examples of other energy discharges include anotherneural stimulation to a different neural target or recharge pulses afterneural stimulation, a pulse for an impedance measurement such as aminute ventilation pulse, and discharges associated with CRM therapysuch as pacing pulses, recharge pulses and defibrillation pulses. Thepresent subject matter prevents neural stimulation from beingsimultaneously applied when another energy discharge is occurring. Someembodiments stagger the neural stimulation with respect to the otherenergy discharge(s) to provide at least a few milliseconds betweenenergy discharges, which prevents electrical interactions between pulseswithout diminishing the effectiveness of the pulses from a physiologicalperspective.

Various aspects of the present subject matter relate to a system.Various embodiments of the system comprise at least one port to connectto at least one lead with at least one electrode, at least onestimulator circuit and at least one controller. The at least onestimulator circuit is connected to the at least one port and is adaptedto deliver neural stimulation to a neural stimulation target using theat least one electrode. The at least one controller is adapted todetermine when another energy discharge other than the neuralstimulation to the neural stimulation target is occurring and to preventdelivery of the neural stimulation simultaneously with the other energydischarge.

Various aspects of the present subject matter relate to a method. Invarious embodiments of the method, neural stimulation is delivered to aneural stimulation target, and another energy discharge is provided. Itis determined when the other energy discharge is occurring. Delivery ofthe neural stimulation to the neural stimulation target is preventedwhen the other energy discharge is occurring.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects will be apparent to persons skilled in the art upon reading andunderstanding the following detailed description and viewing thedrawings that form a part thereof, each of which are not to be taken ina limiting sense. The scope of the present invention is defined by theappended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system including an implantable medical device(IMD) and a programmer, according to various embodiments of the presentsubject matter.

FIG. 2 illustrates a system diagram of an embodiment of an implantablemedical device configured for multi-site stimulation and sensing.

FIG. 3 illustrates an implantable medical device (IMD) having a neuralstimulation (NS) component and cardiac rhythm management (CRM)component, according to various embodiments of the present subjectmatter.

FIG. 4 illustrates a pair of electrodes such as can be used provide anenergy discharge, and a desired current path between the electrodes andthrough tissue.

FIG. 5 illustrates a first pair of electrodes for use in providing afirst desired energy discharge and a second pair of electrodes for usein providing a second desired energy discharge.

FIGS. 6A and 6B illustrates an electrical schematic of a neuralstimulator with two independent pacing circuits and with two energydischarge outputs 638A and 638B, and further illustrates desired currentpaths and undesired current paths, respectively, for the two energydischarge outputs, and further illustrates intended and unintendedcurrent paths.

FIG. 7 illustrates neural stimulation to three neural targets whosestimulation is staggered to prevent simultaneous neural stimulation,according to various embodiments of the present subject matter.

FIG. 8 illustrates neural stimulation to three neural targets whosestimulation is staggered using predetermined time slots for apredetermined time period within a time domain multiplexing scheme toprevent simultaneous neural stimulation, according to variousembodiments of the present subject matter.

FIG. 9 illustrates CRM pacing and neural stimulation over the course ofa cardiac cycle, according to various embodiments of the present subjectmatter.

FIG. 10 illustrates CRM pacing and neural stimulation over the course ofa cardiac cycle, according to various embodiments of the present subjectmatter.

FIG. 11 illustrates a method according to various embodiments of thepresent subject matter.

FIG. 12 illustrates a method according to various embodiments of thepresent subject matter.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto the accompanying drawings which show, by way of illustration,specific aspects and embodiments in which the present subject matter maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present subject matter.Other embodiments may be utilized and structural, logical, andelectrical changes may be made without departing from the scope of thepresent subject matter. References to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope is defined only by the appended claims,along with the full scope of legal equivalents to which such claims areentitled.

Implantable medical devices are capable of having independentprogrammable outputs. If stimulation is delivered simultaneously fromcapacitive coupled outputs programmed to different pacing voltages,unexpected current pathways are created between outputs. Theseunexpected currents can add or subtract from the intended currentpathway. One problem associated with these unexpected current pathwaysfrom simultaneous pacing involves changes in the capture thresholds fromthe expected capture threshold for the electrodes. Stimulating theoutputs one at a time, with a small period of time (e.g. 1 millisecond)separating the end of one stimulation pulse for one output and thebeginning of another stimulation pulse for another output, such that thepacing stimulation does not overlap avoids complex intersite currentpathways.

The present subject matter addresses undesirable interactions that mayoccur when neural stimulation is provided simultaneously with anotherenergy discharge, whether for therapy or diagnostic purposes. Examplesof another energy discharge include another neural stimulation to adifferent neural target, a pulse for an impedance measurement such as aminute ventilation pulse, and a discharge associated with a CRM therapysuch as a pacing pulse, a recharge pulse and a defibrillation pulse. Ifthe algorithms of the therapy(ies) would simultaneously provide neuralstimulation and an energy discharge, the present subject matteroverrides the algorithms to stagger the neural stimulation and the otherenergy discharge. Typically, a few milliseconds is sufficient to preventelectrical interaction. However, a few millisecond discharge typicallywill not diminish the effectiveness from a physiological perspective.

FIG. 1 illustrates a system 100 including an implantable medical device(IMD) 101 and a programmer 102, according to various embodiments of thepresent subject matter. Various embodiments of the IMD 101 includeneural stimulator functions only, and various embodiments include acombination of NS and CRM functions. The IMD can be designed to deliverother therapies, such as drug therapies, along with the neuralstimulation and/or CRM therapies. The IMD and programmer are capable ofwirelessly communicating data and instructions. In various embodiments,for example, the programmer and IMD use telemetry coils to wirelesslycommunicate data and instructions. Thus, the programmer can be used toadjust the programmed therapy provided by the IMD, and the IMD canreport device data (such as battery and lead resistance) and therapydata (such as sense and stimulation data) to the programmer using radiotelemetry, for example.

FIG. 1 illustrates an implantable medical device (IMD). Aspects of thepresent subject matter can be practiced using external devices. FIG. 1also illustrates that IMD communicating with a programmer. The IMD canalso wirelessly communicate directly with a personal digital assistantor other electronic device such as would be used in an advanced patientmanagement (APM) system, which can organize and perform calculationsbased on recorded data, and later provide the data to a programmer.

FIG. 2 illustrates a system diagram of an embodiment of an implantablemedical device configured for multi-site stimulation and sensing. Thisdiagram provides another example of an IMD capable of performing aneural stimulation therapy and a number of CRM therapies. Pacing, asused in the discussion of this figure, relates to electricalstimulation. In various embodiments, the stimulation for a given channelincludes stimulation to capture myocardia, neural stimulation or bothpacing and neural stimulation. Three examples of sensing and pacingchannels, such as can be used in CRM therapy, are designated “A” through“C”. The illustrated channels comprise bipolar leads with ringelectrodes 203A-C and tip electrodes 204A-C, sensing amplifiers 205A-C,pulse generators 206A-C, and channel interfaces 207A-C. Each of thesechannels thus includes a stimulation channel extending between the pulsegenerator, the electrode and a sensing channel extending between thesense amplifier and the electrode. The channel interfaces 207A-Ccommunicate bidirectionally with microprocessor 208, and each interfacemay include analog-to-digital converters for digitizing sensing signalinputs from the sensing amplifiers and registers that can be written toby the microprocessor in order to output pacing pulses, change thepacing pulse amplitude, and adjust the gain and threshold values for thesensing amplifiers. The sensing circuitry detects a chamber sense,either an atrial sense or ventricular sense, when an electrogram signal(i.e., a voltage sensed by an electrode representing cardiac electricalactivity) generated by a particular channel exceeds a specifieddetection threshold. Algorithms, including a number of adjustableparameters, used in particular stimulation modes employ such senses totrigger or inhibit stimulation, and the intrinsic atrial and/orventricular rates can be detected by measuring the time intervalsbetween atrial and ventricular senses, respectively.

The switching network 209 is used to switch the electrodes to the inputof a sense amplifier in order to detect intrinsic cardiac activity andto the output of a pulse generator in order to deliver stimulation. Theswitching network also enables the device to sense or stimulate eitherin a bipolar mode using both the ring and tip electrodes of a lead or ina unipolar mode using only one of the electrodes of the lead with thedevice housing or can 210 serving as a ground electrode or anotherelectrode on another lead serving as the ground electrode. A shock pulsegenerator 211 is also interfaced to the controller for delivering adefibrillation shock via a pair of shock electrodes 212 to the atria orventricles upon detection of a shockable tachyarrhythmia. Channelinterface 213 and sense amplifier 214 provide a connection between themicroprocessor and the switch to receive a sensed signal from a sensor215 for use to guide therapy. Channel interface 217 provides aconnection between the microprocessor 208 and a neural stimulator 218,which provides neural stimulation to the neural stimulation electrodes216.

The controller or microprocessor controls the overall operation of thedevice in accordance with programmed instructions and a number ofadjustable parameters stored in memory 219, including controlling thedelivery of stimulation (including neural stimulation and CRM pacing,defibrillation and recharge pulses) via the channels, interpreting sensesignals received from the sensing channels, and implementing timers fordefining escape intervals and sensory refractory periods. The controlleris capable of operating the device in a number of programmed stimulationmodes which define how pulses are output in response to sensed eventsand expiration of time intervals. Most pacemakers for treatingbradycardia are programmed to operate synchronously in a so-calleddemand mode where sensed cardiac events occurring within a definedinterval either trigger or inhibit a pacing pulse. Inhibited stimulationmodes utilize escape intervals to control pacing in accordance withsensed intrinsic activity such that a stimulation pulse is delivered toa heart chamber during a cardiac cycle only after expiration of adefined escape interval during which no intrinsic beat by the chamber isdetected. Escape intervals for ventricular stimulation can be restartedby ventricular or atrial events, the latter allowing the pacing to trackintrinsic atrial beats. A telemetry interface 220 is also provided whichenables the controller to communicate with an external programmer orremote monitor.

FIG. 3 illustrates an implantable medical device (IMD) 321 such as shownat 101 in FIG. 1 having a neural stimulation (NS) component 322 andcardiac rhythm management (CRM) component 323, according to variousembodiments of the present subject matter. The IMD in FIG. 3 providesanother illustration in addition to the IMD in FIG. 2. The illustrateddevice 321 includes a controller 324 and a memory 325. According tovarious embodiments, the controller includes hardware, software, or acombination of hardware and software to perform the neural stimulationand CRM functions. For example, the programmed therapy applicationsdiscussed in this disclosure are capable of being stored ascomputer-readable instructions embodied in memory and executed by aprocessor. According to various embodiments, the controller includes aprocessor to execute instructions embedded in memory to perform theneural stimulation and CRM functions. The illustrated device 321 furtherincludes a transceiver 326 and associated circuitry for use tocommunicate with a programmer or another external or internal device.Various embodiments include a telemetry coil.

The CRM therapy section 323 includes components, under the control ofthe controller, to stimulate a heart and/or sense cardiac signals usingone or more electrodes. The CRM therapy section includes a pulsegenerator 327 for use to provide an electrical signal through anelectrode to stimulate a heart, and further includes sense circuitry 328to detect and process sensed cardiac signals. An interface 329 isgenerally illustrated for use to communicate between the controller 324and the pulse generator 327 and sense circuitry 328. Three electrodesare illustrated as an example for use to provide CRM therapy. However,the present subject matter is not limited to a particular number ofelectrode sites. Each electrode may include its own pulse generator andsense circuitry. However, the present subject matter is not so limited.The pulse generating and sensing functions can be multiplexed tofunction with multiple electrodes.

The NS therapy section 322 includes components, under the control of thecontroller, to stimulate a neural stimulation target and/or sense ANSparameters associated with nerve activity or surrogates of ANSparameters such as blood pressure and respiration. Three interfaces 330are illustrated for use to provide ANS therapy. However, the presentsubject matter is not limited to a particular number interfaces, or toany particular stimulating or sensing functions. Pulse generators 331are used to provide electrical pulses to an electrode for use tostimulate a neural stimulation target. According to various embodiments,the pulse generator includes circuitry to set, and in some embodimentschange, the amplitude of the stimulation pulse, the frequency of thestimulation pulse, the burst frequency of the pulse, and the morphologyof the pulse such as a square wave, triangle wave, sinusoidal wave, andwaves with desired harmonic components to mimic white noise or othersignals. Sense circuits 332 are used to detect and process signals froma sensor, such as a sensor of nerve activity, blood pressure,respiration, and the like. The interfaces 330 are generally illustratedfor use to communicate between the controller 324 and the pulsegenerator 331 and sense circuitry 332. Each interface, for example, maybe used to control a separate lead. Various embodiments of the NStherapy section only include a pulse generator to stimulate neuraltargets such as baroreceptors, nerve trunks, and cardiac fat pads.

According to various embodiments, the lead(s) and the electrode(s) onthe leads are physically arranged with respect to the heart in a fashionthat enables the electrodes to properly transmit pulses and sensesignals from the heart, and with respect to neural targets to stimulate,and in some embodiments sense neural traffic from, the neural targets.Examples of neural targets include both efferent and afferent pathways,such as baroreceptors, nerve trunks and branches such as the vagus nerveand its cardiac branches, and cardiac fat pads, to provide a desiredneural stimulation therapy. As there may be a number of leads and anumber of electrodes per lead, the configuration can be programmed touse a particular electrode or electrodes.

The leads of the device include one or more leads to provide CRMtherapy, such as atrial pacing, right and/or left ventricular pacing,and/or defibrillation. The device also contains at least on neuralstimulation lead which is placed in an appropriate location. Someembodiments perform neural stimulation and CRM therapy using the samelead. Examples of neural stimulation leads include: an expandablestimulation lead placed in the pulmonary artery in proximity of a highconcentration of baroreceptors; an intravascularly-fed lead placedproximate to a cardiac fat pad to transvascularly stimulate the fat pad;an epicardial lead with an electrode placed in or proximate to the fatpad; a cuff electrode placed around the aortic, carotid, or vagus nerve;and an intravascularly-fed lead placed to transvascularly stimulate theaortic, carotid or vagus nerve. Other lead placements to stimulate otherneural targets may be used.

The controller controls delivery of the electrical pulses using aplurality of parameters for at least one programmed electrical therapyof a first electrical therapy type. The controller is adapted to preventdifferent stimulus, or energy discharges, from occurring simultaneouslywith a neural stimulation.

FIG. 4 illustrates a pair of electrodes such as can be used provide anenergy discharge, and a desired current path 433 between the electrodesand through tissue. However, there can be problems when more than twoelectrodes are present. FIG. 5 illustrates a first pair of electrodes A1and A2 for use in providing a first desired energy discharge via desiredcurrent path 533A, and a second pair of electrodes B1 and B2 for use inproviding a second desired energy discharge via desired current path533B. However, other unintended current paths may be presence if thereis a potential difference between the electrodes. For example, currentflows through current path 534 if there is a potential differencebetween electrodes A1 and B1, such as may occur if a higher voltage CRMtherapy is applied using electrodes A1 and A2 and a lower voltage neuralstimulation therapy is applied using electrodes B1 and B2. Additionally,current flows through current path 535 if there is a potentialdifference between electrodes A2 and B2, through current path 536 ifthere is a potential difference between electrodes A1 and B2, if throughcurrent path 537 if there is a potential difference between electrodesB1 and A2. Currents in these unintended current paths 534-537 caninterfere with the current in the intended current paths 533A and 533B.Depending on the potentials on the electrodes, the unintended currentcan be summed with the intended current or subtracted from the intendedcurrent. The figures illustrate tissue impedance via a simple resistivenetwork. Capacitive and inductive components in the stimulation channelsin the lead(s) and IMD can also provide an adverse interaction for theintended current paths.

FIGS. 6A and 6B illustrates an electrical schematic of a neuralstimulator with two independent pacing circuits and with two energydischarge outputs 638A and 638B, and further illustrates desired currentpaths and undesired current paths, respectively, for the two energydischarge outputs. The illustrated device includes energy sources 639Aand 639B associated with each output. Three electrodes 640A, 640B and640C are schematically illustrated, along with tissue resistancesR_(Tissue) between electrodes 640A and 640B for output 638A and betweenelectrodes 640B and 640C for output 638B. The figure illustrates thatenergy discharge outputs 638A and 638B associated with the twoindependent pacing circuits 641A and 641B share electrode 640B. Thefigure also illustrates a number of switches, capacitors and resistancesto model the independent pacing circuits of the neural stimulator.

FIG. 6A illustrates the desired current paths 642A and 642B for each ofthe independent pacing circuits, and FIG. 6B illustrates the unintendedcurrent paths 643A, 643B and 643C between the two independent pacingcircuits 641A and 642B. There is a strong interaction among independentpacing circuits due to aberrant current paths between the various pacingsites. The aberrant current paths are present during stimulations(neural stimulation, pacing, recharge cycles, and impedancemeasurements. The aberrant current paths corrupt the charge balancebetween the pacing and recharge pulses. This improper charge balanceresults in a significant capture threshold increase of a site with thelowest independent capture threshold. The increase in the capturethreshold is dependent on the pacing impedance, voltage and leadlocation.

The present subject matter relates to an implantable system thatprovides neural stimulation at multiple sites, or both neuralstimulation and CRM therapy (such as pacing, defibrillation, CRT or acombination). Both these functions could be contained in the samedevice, or independent implantable devices that communicate throughlead-based or leadless means.

For example, some system embodiments include a device that includesport(s), stimulator circuit(s), and a controller to control delivery ofboth the neural stimulation and the other energy discharge. Some systemembodiments include a device that includes port(s), stimulatorcircuit(s), a first controller to control delivery of the neuralstimulation, and a second controller to control delivery of the otherenergy discharge, where the second controller is adapted to interruptdelivery of the neural stimulation when the other energy discharge isoccurring. Some system embodiments include a device that includesport(s), stimulator circuit(s), a first controller to control deliveryof the neural stimulation, and a second controller to control deliveryof the other energy discharge, where the first controller is adapted toprevent delivery of the neural stimulation when the other energydischarge is occurring. Some system embodiments include a first deviceto deliver neural stimulation and a second device to deliver anotherenergy discharge and to communicate with the first device, where each ofthe first and second devices include port(s) to connect lead(s),stimulator circuit(s), and controller(s).

The implantable system prevents the simultaneous release of two or moresources of energy, preventing pulse attenuation or reversal that wouldotherwise occur. Examples of the sources of energy include cardiacpacing, neural stimulation, recharging, minute ventilation pulses, etc.Various embodiments stagger the application of neural stimulationtherapy with the application of other therapies. For example, if acardiac pacing is required during a prolonged (e.g. 10 second) period ofneural stimulation, short windows can be created in the neuralstimulation burst during which cardiac pacing could occur. Thus, thepresent subject matter provides a solution for pulse attenuation orreversal that may result from the simultaneous application of neuralstimulation and cardiac pacing.

FIG. 7 illustrates neural stimulation to three neural targets 744A, 744Band 744C, whose stimulation is staggered to prevent simultaneous neuralstimulation, according to various embodiments of the present subjectmatter. In this embodiment, a controller stops a neural stimulationburst (e.g. 744A at 745) before beginning another neural stimulationburst (e.g. 744B at 745). According to this embodiment, the duration ofeach neural stimulation burst is able to vary, since the controllercontrols the starting and stopping of each neural stimulation 744A, 744Band 744C.

FIG. 8 illustrates neural stimulation to three neural targets 844A,844B, 844C, whose stimulation is staggered using predetermined timeslots 845A, 845B, 845C, for a predetermined time period 846 within atime domain multiplexing scheme to prevent simultaneous neuralstimulation, according to various embodiments of the present subjectmatter. The time slots can be of equal duration with respect to eachother, or some time slots can be longer or shorter than other timeslots. If a neural target is to be stimulated, the controller controlsthe delivery of the neural stimulation to remain in the predeterminedtime slot for the neural target. In this illustrated embodiment, thecontroller only needs to apply the different therapies 844A, 844B and844C in its respective time slot, and does not need to determine when afirst therapy is ready to be applied, and interrupt a second therapy toallow the first therapy to be applied.

FIG. 9 illustrates CRM pacing and neural stimulation over the course ofa cardiac cycle, according to various embodiments of the present subjectmatter. Pacing pulses are represented at 947. The illustrated systempaces 947 the right atrium 948, the right ventricle 949, and the leftventricle 950. The figure also illustrates recharge pulses 951 used toreduce an afterpotential resulting from the paces 947.

After a polarizing pulse is applied, an afterpotential of oppositecharge is induced in the tissue (e.g. myocardium) at the interfacebetween the tissue and stimulating electrode. After cathodalstimulation, for example, a negatively charged electrode is surroundedby an excess of positively charged ions, and negatively charged ions arerepelled. Thus, after a stimulation, the electrode-tissue interface ispolarized. The polarization is related to a number of factors, includingthe amplitude and duration of the pacing stimulus, and the radius,surface area, geometry, surface structure, and chemical composition ofthe electrode. The afterpotential is temporary and exponentially decaysto neutrality. The temporary polarization can be represented as avoltage source at the tissue-electrode interface. Problems associatedwith afterpotential include sensing problems and capture thresholdproblems. For example, afterpotentials can cause an inappropriateinhibition of a pacing pulse unless the sensing circuits are suitablyblanked for a time until the afterpotential sufficiently decays. Theafterpotential can also change the capture threshold. For example, if anegative potential is applied to the electrode to provide cathodalstimulation in the presence of a positive afterpotential, the negativepotential needs to be more negative to compensate for the positiveafterpotential and still provide sufficient stimulus to capture themyocardium. The recharge pulse 951 reduces the afterpotential. Duringthe recharge pulse, the electrode polarity is reversed for a period oftime following the pulse, which diminishes the polarization at theinterface between the electrode and myocardium.

Electrode-tissue interfaces can also be polarized after neuralstimulation pulses. A recharge pulse can also be used to reduce theafter potential following neural stimulation.

FIG. 9 also illustrates neural stimulation 952 to two neural targets 953and 954. As illustrated in the figure, only one energy discharge (pace,recharge, neural stimulation) is delivered at a time. That is, theenergy discharges are staggered such that one energy discharge completesbefore another energy discharge begins. The separation between the endof one discharge and the beginning of another discharge can be on theorder of about 1 ms to prevent the undesired current paths betweenelectrodes.

FIG. 10 illustrates CRM pacing and neural stimulation over the course ofa cardiac cycle, according to various embodiments of the present subjectmatter. The figure represents three types of energy discharges. They area pace 1047, recharge 1051 and neural stimulation 1052. Defibrillationpulses and current provided to conduct impedance measurement, such as atransthoracic impedance measurement, are others type of energydischarges. In the illustrated example, the first electrode is paced,then the second electrode is paced, then the first electrode isrecharged to remove the afterpotential, and then the second electrode isrecharged to remove the afterpotential. The neural stimulation isprovided during portions of the cardiac cycle that are not used toprovide the CRM pacing and recharge functions.

FIG. 11 illustrates a method according to various embodiments of thepresent subject matter. In the illustrated embodiment, neuralstimulation is delivered to a neural stimulation target at 1153. Thereare a number of ways in which neural stimulation can be delivered to aneural target. Some embodiments deliver neural stimulation to abaroreceptor. For example, an expandable lead can be intravascularlyplaced in a vessel, such as a pulmonary artery, proximate to abaroreceptor. Some embodiments deliver neural stimulation to a cardiacfat pad. For example, the cardiac fat pad can be stimulated using anintravascularly-fed lead to transvascularly stimulate the cardiac fatpad, or can be stimulated using an epicardial lead to place an electrodein or proximate to the cardiac fat pad for use in stimulating thecardiac fat pad. Some embodiments deliver neural stimulation to a nervetrunk, such as an aortic nerve, a carotid nerve or a vagus nerve. Forexample, the nerve trunk can be stimulated using a nerve cuff placedaround the nerve trunk or using an intravascularly-fed lead totransvascularly stimulate the nerve trunk.

Another energy discharge is provided at 1154. Examples of such energydischarges include pacing pulses from a cardiac rhythm managementtherapy such as a cardiac resynchronization therapy (CRT), adefibrillation shock, a recharge pulse to depolarize an interfacebetween tissue and the electrode, energy discharged to measure impedancesuch as a minute ventilation pulse, and another neural stimulation toanother neural stimulation target. At 1155, it is determined when theother energy discharge is occurring or going to occur. For example, someembodiments receive an interrupt delivered from a CRM module to disableneural stimulation delivery in preparation for an energy discharge fromthe CRM module. As illustrated at 1156, delivery of the neuralstimulation to the neural stimulation target is prevented when the otherenergy discharge is occurring or going to occur. The process returnsfrom 1156 to 1155 to determine if the other energy discharge is stilloccurring. If, at 1155, the other energy discharge is not occurring oran indication is not received that it will be occurring, the processproceeds from 1155 to 1153 to continue delivering the neural stimulationto the target in accordance with the neural stimulation therapy.

FIG. 12 illustrates a method according to various embodiments of thepresent subject matter. At 1257, a time division multiplexing (TDM)scheme is defined for a time period. The TDM scheme defines at leasttime slots A and B within the time period. An example of a time periodis a cardiac cycle, which provide some benefits for devices that applyboth neural stimulation and CRM therapy. Other time periods may be used.For example, a device that provides neural stimulation at multipleneural stimulation targets may use other time periods. It is determinedat 1258 whether neural stimulation is to be delivered and it isdetermined at 1259 whether other stimulation (e.g. pacing, recharging,other neural stimulation, defibrillation, impedance measurement) is tobe delivered. If neural stimulation is to be delivered, the processproceeds from 1258 to 1260 where the neural stimulation is delivered inthe next time slot A. If neural stimulation is not to be delivered, theprocess proceeds from 1258 to 1262. If the other stimulation is to bedelivered, the process proceeds from 1259 to 1261 where the otherstimulation is delivered in the next time slot B. If the otherstimulation is not to be delivered, the process proceeds from 1259 to1262.

One of ordinary skill in the art will understand that, the modules andother circuitry shown and described herein can be implemented usingsoftware, hardware, and combinations of software and hardware. As such,the illustrated modules and circuitry are intended to encompass softwareimplementations, hardware implementations, and software and hardwareimplementations.

The methods illustrated in this disclosure are not intended to beexclusive of other methods within the scope of the present subjectmatter. Those of ordinary skill in the art will understand, upon readingand comprehending this disclosure, other methods within the scope of thepresent subject matter. The above-identified embodiments, and portionsof the illustrated embodiments, are not necessarily mutually exclusive.These embodiments, or portions thereof, can be combined. In variousembodiments, the methods provided above are implemented as a computerdata signal embodied in a carrier wave or propagated signal, thatrepresents a sequence of instructions which, when executed by aprocessor cause the processor to perform the respective method. Invarious embodiments, methods provided above are implemented as a set ofinstructions contained on a computer-accessible medium capable ofdirecting a processor to perform the respective method. In variousembodiments, the medium is a magnetic medium, an electronic medium, oran optical medium.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover adaptations or variations of the present subjectmatter. It is to be understood that the above description is intended tobe illustrative, and not restrictive. Combinations of the aboveembodiments as well as combinations of portions of the above embodimentsin other embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the present subject mattershould be determined with reference to the appended claims, along withthe full scope of equivalents to which such claims are entitled.

What is claimed is:
 1. An implantable neural stimulator for deliveringneural stimulation therapy to a neural stimulation target in a patientand for preventing simultaneous delivery of the neural stimulationtherapy with another energy discharge from another implantable device inthe patient wherein the other implantable device is an independentimplantable device and wherein the implantable neural stimulator has animplantable housing and the other implantable device has anotherimplantable housing, the implantable neural stimulator comprising: astimulator circuit configured to deliver the neural stimulation therapyto the neural stimulation target in the patient; and a controllerconfigured to control the stimulator circuit to stimulate the neuraltarget, determine when neural stimulation is to be delivered and controlthe stimulator circuit to stimulate the neural target, and preventdelivery of the neural stimulation during the other energy dischargefrom the other implantable device in the patient.
 2. The implantableneural stimulator of claim 1, wherein the controller is configured towait for the other energy discharge from the other implantable device tocomplete before beginning a neural stimulation burst to prevent deliveryof the neural stimulation during the other energy discharge from theother implantable device in the patient.
 3. The implantable neuralstimulator of claim 1, wherein the implantable neural stimulator isconfigured to communicate with the other implantable device.
 4. Theimplantable neural stimulator of claim 3, wherein the controller isconfigured to use communication with the other implantable device toprevent delivery of the neural stimulation during the other energydischarge from the other implantable device in the patient.
 5. Thesystem of claim 1, wherein the other energy discharge includes an energydischarge to capture myocardial tissue from a cardiac rhythm management(CRM) therapy.
 6. The system of claim 5, wherein the energy dischargefrom the CRM therapy includes a pacing pulse.
 7. The system of claim 5,wherein the controller is configured to interrupt neural stimulationduring the energy discharge to capture myocardial tissue.
 8. The systemof claim 1, wherein the other energy discharge from the otherimplantable device in the patient includes a defibrillation shock. 9.The system of claim 1, wherein the other energy discharge from the otherimplantable device in the patient includes a recharge pulse todepolarize an interface between tissue and the electrode.
 10. The systemof claim 1, wherein the other energy discharge from the otherimplantable device in the patient includes energy discharged to measureimpedance.
 11. The system of claim 1, wherein the other energy dischargefrom the other implantable device in the patient includes neuralstimulation to another neural stimulation target in the patient.
 12. Animplantable neural stimulator for delivering neural stimulation therapyto a neural stimulation target in a patient and for preventingsimultaneous delivery of the neural stimulation therapy with anotherenergy discharge from another implantable device in the patient whereinthe other implantable device is an independent implantable device, theimplantable neural stimulator comprising: a stimulator circuitconfigured to deliver the neural stimulation therapy to the neuralstimulation target in the patient; and a controller configured tocontrol the stimulator circuit to stimulate the neural target, determinewhen neural stimulation is to be delivered and control the stimulatorcircuit to stimulate the neural target, and prevent delivery of theneural stimulation during the other energy discharge from the otherimplantable device in the patient, wherein the controller is configuredto interrupt a neural stimulation burst to prevent delivery of theneural stimulation during the other energy discharge from the otherimplantable device in the patient.
 13. A method for stimulating a neuralstimulation target using an implantable neural stimulator that has animplantable housing in a patient in whom another implantable stimulationdevice that has another implantable housing is implanted wherein theimplantable neural stimulator and the other implantable stimulationdevice are independently-controlled devices such that the implantableneural stimulator includes a controller to control neural stimulationfrom the neural stimulator and the other implantable stimulation deviceincludes another controller to control an energy discharge from theother implantable stimulation device, comprising: delivering the neuralstimulation to the neural stimulation target using the implantableneural stimulator; and preventing delivery of the neural stimulation tothe neural stimulation target when the other stimulation device providesthe energy discharge.
 14. The method of claim 13, wherein preventingdelivery of the neural stimulation when the other stimulation deviceprovides an energy discharge includes staggering delivery of the neuralstimulation with the energy discharge.
 15. The method of claim 13,wherein preventing delivery of the neural stimulation to the neuralstimulation target when the other stimulation device provides an energydischarge includes delivering neural stimulation in a firstpredetermined time slot, wherein the energy discharge is provided duringanother predetermined time slot in a time division multiplexing scheme.16. The method of claim 13, wherein preventing delivery of the neuralstimulation when the other stimulation device provides an energydischarge includes responding to an interrupt to prevent delivery of theneural stimulation when the other stimulation device provides an energydischarge.
 17. The method of claim 13, wherein preventing delivery ofthe neural stimulation to the neural stimulation target when the otherstimulation device provides an energy discharge includes interrupting aneural stimulation burst to prevent delivery of the neural stimulationwhen the other stimulation device provides an energy discharge.
 18. Themethod of claim 13, wherein preventing delivery of the neuralstimulation to the neural stimulation target when the other stimulationdevice provides an energy discharge includes waiting for the energydischarge to complete before beginning a neural stimulation burst. 19.The method of claim 13, wherein the discharge from the other stimulationdevice includes a pacing pulse from a cardiac rhythm management therapy.20. The method of claim 13, wherein the energy discharge from the otherstimulation device includes a defibrillation shock.
 21. The method ofclaim 13, wherein the energy discharge from the other stimulation deviceincludes a recharge pulse to depolarize an interface between tissue andthe electrode.
 22. The method of claim 13, wherein the energy dischargefrom the other stimulation device includes energy discharged to measureimpedance.
 23. The method of claim 13, wherein the energy discharge fromthe other stimulation device includes another neural stimulation toanother neural stimulation target.
 24. The method of claim 13, whereindelivering neural stimulation to a neural stimulation target includesstimulating a baroreceptor, an aortic nerve, a carotid nerve or a vagusnerve.